This invention relates to an engine oil degradation detector that detects degradation of engine oils used for an internal combustion engine such as an engine used in automobiles.
The engine oil is used for automotive engines or other internal combustion engines to lubricate contiguous components therein in relative motion. The engine oil becomes degraded with use, and thus need be changed as appropriate. It is conventionally recommended that the engine oil be changed when a specific time has passed or when a specific distance has been traversed.
However, various factors combine to cause the degradation of the engine oil in actuality. For example, unless the internal combustion engine has been driven, it turns out, even after a long time has passed since the engine oil was last changed, that the engine oil has not yet been degraded so much. Likewise, rough driving would rapidly degrade the engine oil, irrespective of a shorter distance traveled. Thus, as is often the case, the degradation of the engine oil could not be precisely detected on a basis of a lapse of time or a distance traveled. In view of these circumstances, Japanese Laid-Open Patent Application, Publication No. 62-203915 A, discloses a method of detecting degradation of oils with consideration given to a driving manner under the title, xe2x80x9cMETHOD FOR INDICATING NECESSITY OF CHANGING ENGINE OILxe2x80x9d. This method employs a temperature of the oil as a factor for determining degradation of the oil. The temperature is monitored to add some counts to the measurement of the effective number of revolutions of an engine when the temperature of oil is considerably higher or considerably lower than a predetermined temperature. Then, the effective numbers of revolutions are added up, and when the integrated number of revolutions reaches a predetermined specific value, it is determined that the time has come when the engine oil should be changed.
However, the above-described conventional technique employs an oil temperature sensor that detects a temperature of oil to determine how the oil is degraded. The oil temperature sensor is dedicated to the determination of the degradation of oil, and thus the conventional technique causes increase in the number of parts as the oil temperature sensor is to be provided. The increase in the number of parts entails increase in cost, additional space required for attachment of the parts, and other disadvantages.
The above disclosure indicates that the oil temperature may be worked out from any other predetermined value, but not refers to a specific methodology therefor.
Therefore, there is a need to reduce the number of parts in an engine oil degradation detector, and it is an object of the present invention to provide an engine oil degradation detector capable of estimating a temperature of the oil without using an oil temperature sensor.
According to one aspect of the present invention, which may eliminate the above disadvantages and achieve the above object, there is provided an engine oil degradation detector as set forth in claim 1 that works out a use level of an engine oil in accordance with a driving manner of the internal combustion engine. The use level of the engine oil indicates how much the engine oil in an internal combustion engine has been used. The engine oil degradation detector includes an engine oil temperature estimation means that estimates a temperature of the engine oil. The use level of the engine oil is corrected with an engine oil degradation coefficient obtained according to the temperature of the engine oil estimated by the engine oil temperature estimation means. The engine oil degradation detector integrates the corrected use levels of the engine oil, and determines that a time to change the engine oil has come when the integrated use level reaches a predetermined value indicating a usable life of the engine oil. The engine oil estimation means works out an estimated engine oil temperature based upon a cooling water temperature of cooling water that cools the internal combustion engine, and an open/closed state of a control valve provided in a cooling water channel.
According to the invention as in claim 1, the engine oil temperature is estimated based upon the cooling water temperature of the cooling water and the open/closed state of the control valve. Therefore, an oil temperature sensor that detects the engine oil temperature is not required, and thus the number of parts may be reduced. Moreover, the change in temperature of the cooling water and the engine oil is largely dependent upon the open/closed state of a control valve, and thus the temperature of the engine oil may be accurately estimated based upon the open/closed state of the control valve.
According to another aspect of the present invention, as set forth in claim 2 that depends upon claim 1, the engine oil temperature estimation means works out the estimated engine oil temperature in accordance with elapsed time of driving of the internal combustion engine, and the elapsed time is corrected in accordance with a driving manner of the internal combustion engine when the control valve is closed.
According to the invention as in claim 2, correction is made to a lapse of time based upon a driving manner using the open/closed state of the control valve that changes with a lapse of time. Therefore, the difference in tendency of the oil temperature increase may accurately be reflected on the estimate.
According to another aspect of the present invention, as set forth in claim 3 that depends upon claim 1, the engine oil temperature estimation means corrects the cooling water temperature in accordance with a driving manner of the internal combustion engine, and works out the estimated engine oil temperature based upon the corrected cooling water temperature.
According to the invention as in claim 3, the water temperature is corrected in accordance with a driving manner of the internal combustion engine when the control valve is open. Therefore, the difference in tendency of the temperature increase between oil and water may be corrected, so that the oil temperature may accurately be estimated.
According to another aspect of the present invention, as set forth in claim 4 that depends upon claim 1, the engine oil temperature estimation means works out an initial value of the estimated engine oil temperature in accordance with a soaking state of the internal combustion engine.
According to the invention as in claim 4, an initial value of the estimated engine oil may be set in accordance with a soaking state, i.e., a standby state that appears from suspension until restarting of the internal combustion engine. Therefore, the temperature of the engine oil may accurately be estimated even when the internal combustion engine is started soon after the internal combustion engine is stopped.